It won't help you improve your vocabulary, but Ben West and Felix Heyes' Google dictionary will keep you up to speed on internet fads and memes. That's because instead of definitions, the book's pages are populated with Google Image search results.
Now, replacing the definitions with images for 21,000 popular words sounds incredibly tedious. Which is why the artists used a couple of PHP scripts that first took all the words in the dictionary and downloaded an image for each one, and then automatically laid them out in alphabetical order into a series of columns. The resulting massive PDF was then professionally printed and bound with a golden Google logo stamped on the cover.
The thick tome probably isn't for the feint of heart, though. As West points out, "I would estimate about half of the book is revolting medical photos, porn, racism or bad cartoons." Which is probably not what Noah Webster originally had in mind. [Crap is Good via Creative Applications]